Some communication systems allow the user of a device, such as a personal computer or mobile device, to conduct voice or video calls over a packet-based computer network such as the Internet. Such communication systems include voice or video over internet protocol (VoIP) systems. These systems are beneficial to the user as they are often of significantly lower cost than conventional fixed line or mobile cellular networks. This may particularly be the case for long-distance communication. To use a VoIP system, the user installs and executes client software on their device. The client software sets up the VoIP connections as well as providing other functions such as registration and authentication. In addition to voice communication, the client may also set up connections for other communication media such as instant messaging (“IM”), SMS messaging, file transfer and voicemail.
During real time communication of audio/video, downloading and uploading of content can occur during the calls. For instance, a service provider may choose to distribute content (e.g. advertisements) to the users, or the users may share content such as photos, screenshots, and files. The distribution of content is typically based on the Hypertext Transfer Protocol (HTTP) or the Hypertext Transfer Protocol Secure (HTTPS) application protocols, with Transmission Control Protocol (TCP) as the default underlying transport protocol.